1. Field of the Invention
This invention relates to a packing bag and manufacturing method for the same.
2. Description of the Related Art
Conventionally, the applicant of the present application has proposed a packing bag formed by welding a sheet material of synthetic resin to tightly seal and preserve stored articles with sanitation (refer to Japanese Patent No. 5715283).
In the packing bag disclosed by Japanese Patent No. 5715283, as shown in FIG. 22, a heated blade 41 contacts an obverse face 40a of a sheet material 40 to form a half-cut V-shaped groove 42, and a separation-prepared line portion to be separated is formed with the V-shaped groove 42.
However, in the production process, the sheet material 40 may be oscillated up and down because the V-shaped groove 42 is formed with continuously running the sheet material 40 of belt, and it is difficult to form the V-shaped groove 42 with a constant depth dimension D in a longitudinal direction of the sheet material 40.
As shown in FIG. 23, tensile force F, needed for separation of the separation-prepared line portion, becomes unstable where a depth dimension D1 of the V-shaped groove 42 is too small and the separation can't smoothly conducted. And, as shown in FIG. 24, when a depth dimension D2 becomes excessive, the sheet material 40 may be penetrated, the separation-prepared line is broken on an unintended position and the tight sealing can't be kept.
Therefore, it is an object of the present invention to provide a packing bag with which the separation-prepared line can be smoothly separated with a constant tensile force and the tight sealing is certainly kept.